A sidelink communications mode refers to that a packet needs not to pass a core network and an eNB, and a communications link may be directly established between UE1 and UE2 for communications. A sidelink discovery process is generally performed before performing sidelink communications. For example, UE2 needs first to discover whether UE1 is near before transmitting information to UE1 in the sidelink communications mode. FIG. 1 is a schematic diagram of discovering or establishing the sidelink communications, in which a case where two UEs (UE1 and UE2) are under coverage of an eNB is shown. FIG. 2 is another schematic diagram of discovering or establishing the sidelink communications, in which a case where one UE (UE1) under coverage of an eNB and another UE (UE2) not under the coverage of the eNB is shown. And FIG. 3 is a further schematic diagram of discovering or establishing the sidelink communications, in which a case where two UEs (UE1 and UE2) not under coverage of an eNB is shown.
V2X (vehicle-to-everything) communications is one of sidelink communications modes, which includes three types of communications modes: V2V (vehicle-to-vehicle) communications, V2I (vehicle-to-infrastructure) communications and V2P (vehicle-to-pedestrian) communications. FIG. 4 is a schematic diagram of these three types of communications modes. In a V2V scenario, two terminals with a relatively short distance therebetween may transmit information on V2V after being authorized by an E-UTRAN (evolved UNTS terrestrial radio access network). The information on V2V may include information on a location, and a terminal attribute, etc. A size of the information on V2V may also be variable. Transmission of the information on V2V may be performed in a direct manner, that is, it may be transmitted by no infrastructure; or, it may be transmitted via an infrastructure, such as an RSU (road side unit).
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.